Stable anionic polymerization initiator

ABSTRACT

The sequential reaction of m-diisopropenylbenzene, an alkyllithium and butadiene or isoprene in the presence of 0.01 to 1.0 mole of a tertiary amine per mole of mdiisopropenylbenzene/alkyllithium adduct in a hydrocarbon solvent yields stable solutions of anionic polymerization initiators suitable for the polymerization of dienes.

United States Patent Foss et al. Sept. 2, 1975 [54] STABLE ANIONIC POLYMERIZATION 3.234.284 2/1966 Beumel. Jr. ct al 260/583 R INITIATOR 3.321.479 5/1967 Eberhard! Ct 211. 260/583 R X 3.734.963 5/1973 Langcr. Jr. et a1 260/563 R Inventors: Robert P. Foss, Hockessin; Henning W. Jacobson, Wilmington. both of Del.

E. I. Du Pont de Nemours and Company. Wilmington. Del.

Filed: Nov. 23, 1973 Appl. No.: 418,578

Assignee:

References Cited UNITED STATES PATENTS 2/1966 Beumel. Jr. ct al 260/583 R Primary [:Irunzirwr-Joseph P. Brust [57] ABSTRACT The sequential reaction of m-diisopropenylbenzene. an alkyllithium and butadiene or isoprene in the presenqe of 0.01 to 1.0 mole of a tertiary amine per mole of m-diisopropenylbenzene/alkyllithium adduct in a hydrocarbon solvent yields stable solutions of anionic polymerization initiators suitable for the polymerization of dienes. r

4 Claims. No Drawings STABLE ANIONIC POLYMERIZA'IION INITIATOR BACKGROLNI) ()F IHE INVENTION l. Field of Invention y This invention relates to hydrocarbon-soluble dian ionic initiator systems prepared from an alkyllithium. m-diisopropenylbenzene, butadicne or isoprene and a tertiary alkylamine, which have unique stability.

2. Description of the Prior Art Dilithioisoprene and dilithio-d-methylstyrene oligomers and their use as anionic polymerization initiators are disclosed by Karoly (ACTS Polymer Preprints. September 1969, I0, No. 2). Fetters and Morton (Macromolecules 1969, 2, 453) disclose l,4-dilithiol,l.4,4- tetraphenylbutane capped with low molecular weight polyisoprene as an anionic initiator, Dit'unctional organolithium initiators available from Lithium Corporation of Americainclude DiLi-lA,-composed ofdilithium oligomers of isoprene, *DiLi-B," composed of a-lithio-substituted dialkylbcnzene monomers and oligomers, and DiLi4. composed of an isoprene adduct 0f 3- and 4- '(lithiomethyl) -1-( l-lithio-3- methylpentyl) benzene (cf. Kamienski, Polymer Preprints, First Akron Summit Polymer Conference,Sym' posium on Anionic Polymerization, University of Ak ron, June 1970, p. 24; Lithium Corporation of America Product Bulletins I91 and 192; German Pat. No. 2,()63,642).These DiLi" initiators contain hydrocar bon solvents (benzene,cyclohexane, n-hexane) and triethylamine in a mole ratio to lithium of about 4: l. The coassigned Foss application Ser. No. 324,502 (now US. Pat. No. 3,821,331, issued June 28, I974) discloses an anionic initiator systemwhich is acyclohexane solution of l,3 bis(l-lithio-l,3-dimethylpentyl) benzene [prepared from sec-butyllithium and m-diisopropenylbenzene] containing three equivalents of tri ethylamine per equivalent of lithium.

SUMMARY OF THE INVENTION The products of this invention are stable,'hydrocarbon-soluble, dianionic polymerization initiators derived by sequential reaction of m-diisopropenylbenzene, an alkylli thium and butadiene or isoprene in a suitable hydrocarbon solv'ent containing a specified amount of a tertiary alkylamine.

These products can be represented as follows:

DETAILS OF THE INVENTION The initiators of the invention are readily prepared in sequential fashion in a hydrocarbon solvent under anhydrous conditions and an inert atmosphere. The solvent and alkylamine. in carefully measured amounts. are initially blended in a suitable reactor: the alkyllithium, whichis of known concentration and preferably in a hydrocarbon solvent such as n'hexane is added; and the diisopropeny lbenzene, in precisely a l:l equivalent ratio (lpZ mole ratio) with the alkyllithium. is then introducedgradually over a period of about 15 minutes with stirring at room temperature. The reaction mixture immediately assumes a red color. After the addition ofdiisopropenylbenzene is complete, the reactionniixture is stirred until no residual unsaturation can be detected by nmr. The alkadiene monomer is finally added rapidly (in one portion) with stirring; the red color begins to fade; and after about one hour at room temperature the initiator preparation, which has a light red color, is considered to be complete and is recorded as being Zero hours in age. The reaction mixture is stored in the original reactor-container at room temperature under dry nitrogen.

The solvent used in the preparation can be any normally liquid hydrocarbon which is nonreactive with an alkyllithium, Representative suitable solvents are nhexane and cyclohexane.

The reaction is normally carried out at room temperature and essentially atmospheric pressure, but can be accomplished without trouble at any combination of temperature 'under about 5 0 and pressure which will maintain the reaction mixture in homogeneous fluid conclition.' "Secondary 'or tertiary alkyllithiums corresponding to R'Li are used in making the products. Representative alkyllithiums are sec-butyllithiurn, tbutyllithium, isopropyllithium. l-methylpentyllithium, cyclohexyllithium and menthyllithium. Sec-butyllithium is a preferred alkyl-lithium, and accordingly the secbutyl group is a preferred value of R.

The tertiary amine component of the product, represented by (R MN, can be any saturated tertiary lower alkylamine. Representative amines are trimethylamine, triethylamine (preferred. R being ethyl), tributylamine and trihexylaminef The products of the invention are termed polyalkadiene-capped l,3-bis( l -lithio'sec-all yl )benzene initiators. Uncapped bis(lithioalkyl )benzene initiators are well known '(cf, DiLi-B"), and polyisoprene-capped 1,4-dilithio-l, l,4,4-tetraphenylbutane initiator is also known (cf, Fetters and Morton). The latter polyisoprenyl inititator contains no tertiary amine, may optionally contain an ether cosolvent, and has polyisoprenyl seg ments containing more than l0 isoprene monomer units. i y i The distinctive, sought-for but generally elusive. advantage of the initiator of this invention is long term stability of its solutions in a hydrocarbon solvent. This stability includes both physical and chemical stability as demonstrated by retention of clarity with no formation of precipitate and by retention of a consistent preas an initiator forpreparation of polyalkadienes'is outstanding in that the polydiene products have predict SPECIFIC EMBODIMENTS OF THE- lNVENTION The following examples illustrate. the preparation and properties'of a representative initiator of this invention and comparison of its performance with closely similar but much less consistent initia'torstypical in behavior "of some in the prior art. In these examples temperatures are given in degr'ees'centigrade. In the interest of simplified yet fully explanatory nomenclature the various initiators are identified by the. code DlPLlT-mjz wherein i i DIP represents n diisopr op enylbenzene L represents lithium I i r l represents isoprene T} represent triethylamine I nurepresents moles of isoprene per gram-atom of lithium (similar tom in the preceding general forimura) v, I n represents moles of triethylamine per gram-atom of lithium (similarto 2:1 in the preceding general formula) EXAMPLE I DIPLIT 5.0.1 Initiator I 'A SOO-ml bottle containiii ga magnetic stirring bar was dried overnight at 150, closed under nitrogen with a serum stopper and arranged for maintenance of an inert atmosphere by means of a hypodermic needle piercing the stopper connected through a'T-tube to a supply of argon and an air-excluding bubbler The bottle was charged via a hypodermic syringe successively with 430 ml of cyclohexane, 41.5 ml (l.2lN in hexane. 50 meq) of sec-butyl-lithium, 0.7 ml ('5 meq) of triethylamine and 4.35 ml (50 meq) of m-diisoafter the addition was complete the red solution was stirred overnight at room temperature. The final reaction mixture, after about 18 hours, was found by nmr to be free of residual unsaturation, indicatingcomplete reaction of the dissopropenylbenzene. At this stage ml (250 me'q) of freshly distilled isoprenewas added rapidly with stirring; The color of the solution began to fade and after one hour; though still red, was much lighter than before. At this point the initiator preparation, close to (UN in concentration, was considered complete" and to be zero hours in age, The bottle containing the initiator, after removal of the argon-atmosphere-maintaining hypodermic needle, was stored under nitrogen at room'temperature in a dry box'.

Using the above general procedure with appropriate amounts of triethylamine and without any isoprene uncapped Dinar-0,0, -0 ,.1'; -'0;{.2; .-.0,.4, -0,1; 0,3 l and -(),l0 initiators were also prepared. a

Polyisoprene Prepared with DIPLIT- S I Initiator A dry 250-ml flask containing 'a magnetic stirring bar and closed with a serumstopper was arranged for main tenance of an inert atmosphere through a side arm attached to a glass T-tube', one arm of which wasieonnected to a source of argon and the other to a bubbler. The flaskwas dried byfiamingitout under a heavy. flow of argon and then was allowed to cool toroorn temper: ature. The flask was then charged by means of a hyp 0- dermic syringe with 100 ml of cyclohexane and 15 ml (150 meq), of isoprene." The cyclohexane had been freshly purified as in ,Example 1 and the-isoprene had been purified by adding' n-butyllithium to dry, polymer: izationsgrade isoprene and allowing the heat of, the resulting [polymerization to. distill monomeric isoprene into a-dry, ice-cooled vessel protected from the atmo sphere by argon. After the isoprene had been added the stirring bar was activated, the. solution the flaskiwas heated to 60 by means of an'oil bath, and; 3 5 111041%, 0.8 meq) of the DI P LET- 5 ,O.l initiator solution of Ex ample l was added via a hypodermic syringe. Stirring of the polymerization mixture, at 60 was continued for 2 hours, atwhich time polymerization was terminated by addition of a small volume of methanol diluted with tetrahydrofuran. Thesolventwas then substantially removed under vacuum and the residualpolymer was redissolved in'tetr'ahydr'ofuran. 1 I

The tetrahydrofuranv solution of polyisoprene wasanalyzed gel permeation chromatography (GPC) for characterization by M, (number average molecular weight), M (weightaverage molecular weight) and d (dispersity =M,. /M, The theoreticalmolecularlyveight of the polyi's'oprene prepared by thisrecipe is calcu flated at about 25 M. U I r r Analytical characterization by GPC of polyisoprenes prepared as described above with the DIPLIT-5,.l initiator of-Example l at various stages in its aging showed In contrast to the above, uncapped (m=0) DIPLIT initiators were found unable to give predictable or consistent results over a reasonable aging period. This is illustrated by the data in Table II for polyisopr'enes pre- 6 pared with uncapped initiators by the procedure of Ex- R is secondary alkyl, tertiary alkyl or cycloalkyl ample 2. of up to 10 carbon atoms;

TABLE II DIPLIT Age GPC Data Remarks (m. n) (Days) M MA, d

() U 37 M 40 M l 2 initiator showed rapid formation of precipitate in its initial solution .I l) 25 M 3] M L23 Fresh initiator ()K.

4 33 M 42 M 1.18 but showed precipitate l l 43 M (12 M 1.47 in aged samples l) U 26 M 37 M L41 Initiator showed pre- 3 32 M 4N M 137 cipitatc in aged 7 47 M h) M 1.47 samples U. l l 20 M 72 M 177 recipitate in aged 1 I 32 M 4) M L50 samples of initiator (I "l 2U 22 M I04 M 70 Polymers showed hroatl 52 20 M 55 M 2.] l himodal GPC curves 0 4 l l 25 M (12 M 147 Polymer showed broad bimodal (PPC curves (1 IO U 20 M St! M 2.50 Polymers shoncd broad 2 II M 52 M 2.47 bimodal GPC curves 4 3 M 53 M 2.2K

Since any obvious modifications will occur to one R is alkyl of l to 6 carbon atoms; skilled in the art, we intend to be bound solely by the m i km t g Of and appended claims. 25 n is a number in the range 0.01 to 1.0 inclusive. We claim: 2. Compound of claim 1 wherein R is methyl. 1. A compound having the formula: 3. Compound of claim 2- wherein R is scc-butyl.

2 Li (R )3N wherein; 4. Compound of claim 3- wherein R is ethyl.

RisHormethyl; 

1. A COMPOUND HAVING THE FORMULA:
 2. Compound of claim 1 wherein R is methyl.
 3. Compound of claim 2 wherein R1 is sec-butyl.
 4. Compound of claim 3 wherein R2 is ethyl. 